Directions: Simplify by multiplying the expressions.
10. (5r + 7s)(5r - 7s)

11. (a + 1/2)(a - 1/2)

12. (x2 + 8)(x2 - 8)

13. (r + .5)(r - .5)

14. (ab + 8)(ab - 8)

15. (3/4c + d)(3/4c – d)

16. (r3 - 2s2)(r3 + 2s2)

17. (a + 5)(a – 5)(a2 – 25)

18. (a + b)(a – b) (a2 – b2)

19. (5c2d3 – 7e5)(5c2d3 – 7e5)

20. (m2 + n2)(m2 – n2)(m4 +n4)